Method of forming a bonding pad structure

ABSTRACT

A semiconductor device having a semiconductor substrate and a bonding pad portion formed on the semiconductor substrate, the bonding pad portion having: an insulating film formed on the semiconductor substrate and a first-level conductive pad layer of a large island shape formed on the insulating film; first-level to (n−1)-level (n is an integer of 3 or larger) interlayer insulating films formed on and over the insulating film; second-level to n-level conductive pad layers formed on the interlayer insulating films in areas generally corresponding to an area where the first conductive pad layer was formed; a plurality of small diameter first through holes from the first-level to (n−1) level formed through the first-level to (n−1) level interlayer insulating films in areas generally corresponding to an area where the first conductive pad layer; a plurality of first contact plugs filled in the small diameter first through holes from the first-level to (n−1)-level, the first contact plugs at each level being conductive and electrically connecting two conductive pad layers adjacent along a normal to a surface of the semiconductor substrate, among the first-level to n-level conductive pad layers disposed in and on the first-level to (n−1)-level interlayer insulating films; an n-level interlayer insulating film formed on the (n−1)-level interlayer insulating film and covering the n-level conductive pad; a large diameter through hole formed though the n-level interlayer insulating film in an area corresponding to an area where the n-level conductive pad was formed; the large diameter through hole having a size corresponding to the n-level conductive pad to expose a substantial upper surface of the n-level conductive pad; and a bonding pad formed on the n-level interlayer insulating film and n-level conductive pad via the large diameter through hole.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of Application Ser. No. 11/073,753,filed Mar. 8, 2005, now U.S. Pat. No. 7,067,928 which is a Divisional ofApplication Ser. No. 09/866,421, filed May 25, 2001, now U.S. Pat. No.6,921,714 which is a Divisional of Application Ser. No. 09/407,910,filed Sep. 29, 1999, and issued as U.S. Pat. No. 6,297,563 on Oct. 2,2001, the entire disclosures of each of which are incorporated herein byreference.

This application is based on Japanese patent application No. HEI10-294459 filed on Oct. 1, 1998, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The present invention relates to a bonding pad structure of asemiconductor device such as an LSI, and more particularly to a bondingpad structure having n (n is an integer of 3 or larger) pad layers and(n−1) interlayer insulating films.

b) Description of the Related Art

A most common bonding pad structure has large bonding pads formed on thehighest-level insulating film among a plurality of insulating films.With such a bonding pad lamination structure, if a lamination filmincluding a coated insulating film such as organic or inorganic SOG(spin on glass) is used as the insulating film or films under the padlayer, peel-off or cracks of the coated insulating film may occurbecause of heat and pressure during the bonding, thereby lowering thereliability.

In order to solve this problem, semiconductor devices having a bondingpad area such as shown in FIGS. 8 to 11 are known (refer toJP-A-9-219451).

In the semiconductor device shown in FIG. 8, a first-level (first-layer)insulating film 2 is formed on the surface of a semiconductor substrate1. On this first-level insulating film 2, a plurality of first-levelwiring layers 3 a and a plurality of first-level pad layers 3 b areformed. The wiring layer 3 a is formed in an inner wiring area Aincluding an integrated circuit formed on the semiconductor substrate 1.The pad layer 3 b is formed in a bonding pad area B disposed around theinner wiring area A.

On the first-level insulating film 2, a first-level interlayerinsulating film 4 is formed covering the plurality of wiring layers 3 aand pad layers 3 b. The upper surface of the first-level interlayerinsulating film 4 is planarized by chemical mechanical polishing (CMP).A contact hole 4A and a plurality of contact holes 4B are formed throughthe first-level interlayer insulating film 4 by photolithography and dryetching in the areas corresponding to the wiring layer 3 a and pad layer3 b. First-level contact plugs 5 a and 5 b are filled in the contactholes 4A and 4B. These contact plugs 5 a and 5 b are formed by forming aconductive layer of tungsten (W) or the like on the insulating film 4and in the contact holes 4A and 4B, and thereafter etching back theconductive layer until the upper surface of the insulating film 4 isexposed.

On the first-level interlayer insulating film 4, a second-level wiringlayer 6 a and a second-level pad layer 6 b are formed. The wiring layer6 a is connected via the contact plug 5 a to the wiring layer 3 a, andthe pad layer 6 b is connected via a plurality of contact plugs 5 b tothe pad layer 3 b.

On the first-level interlayer insulating film 4, a second-levelinterlayer insulating film 7 is formed covering the second-level wiringlayer 6 a and second-level pad layer 6 b. The upper surface of thesecond-level interlayer insulating film 7 is planarized by CMP. Acontact hole 7A and a plurality of contact holes 7B are formed throughthe second-level interlayer insulating film 7 by photolithography anddry etching in the areas corresponding to the second-level wiring layer6 a and second-level pad layer 6 b. Second-level contact plugs 8 a and 8b are filled in the contact holes 7A and 7B. These contact plugs 8 a and8 b are formed by a process similar to that of forming the first-levelcontact plugs 5 a and 5 b described above.

On the second-level interlayer insulating film 7, a third-level wiringlayer 9 a and a third-level pad layer 9 b are formed. The third-levelwiring layer 9 a is connected via the second-level contact plug 8 a tothe second-level wiring layer 6 a, and the third-level pad layer 9 b isconnected via a plurality of second-level contact plugs 8 b to thesecond-level pad layer 6 b.

In the semiconductor device shown in FIG. 9, the wring structure in theinner wiring area A is similar to that in the inner wiring area A shownin FIG. 8. In FIG. 9, like elements to those shown in FIG. 8 arerepresented by using identical reference symbols, and the descriptionthereof is omitted.

In the bonding pad area B shown in FIG. 9, the insulating film 4 isformed on the insulating film 2, and the insulating film 7 is formed onthe insulating film 4. On the insulating film 7, a pad layer 9 b isformed by using the same process as that of forming the wiring layer 9a.

In the semiconductor device shown in FIG. 10, the wring structure in theinner wiring area A is similar to that in the inner wiring area A shownin FIG. 8. In FIG. 10, like elements to those shown in FIG. 8 arerepresented by using identical reference symbols, and the descriptionthereof is omitted.

In the bonding pad area B shown in FIG. 10, the insulating film 4 isformed on the insulating film 2, and on the insulating film 4 the padlayer 6 b is formed by using the same process as that of forming thewiring layer 6 a.

On the insulating film 4, the insulating film 7 is formed covering thewiring layer 6 a and pad layer 6 b. The upper surface of the insulatingfilm 7 is planarized by CMP. Contact holes 7A and 7B are formed throughthe insulating film 7 by photolithography and dry etching in the areascorresponding to the wiring layer 6 a and layer 6 b. The contact hole 7Sis made larger in size than the contact hole 7A for the later process ofbonding a bonding wire.

After a conductive layer of W or the like is formed on the insulatingfilm 7 and in the contact holes 7A and 7S, the conductive layer isetched back until the upper surface of the insulating film is exposed. Acontact plug 8 a made of conductive material such as W is thereforeformed in the contact hole 7A. At this time, although a thin conductivelayer (not shown) is left on the side wall of the contact hole 7S, mostof the conductive layer are etched and removed during the etch-backprocess so that the upper surface of the pad layer 6 b is exposed in thecontact hole 7S.

A wiring layer is deposited on the insulating film 7, covering thecontact plug 8 a and the contact hole 7S, and patterned to form a wiringlayer 9 a and a pad layer 9 b. The pad layer 9 b directly contacts thepad layer 6 b in the contact hole 7S.

In the semiconductor device shown in FIG. 11, on the insulating film 2covering the surface of the substrate 1, the first-level wiring layer 3a and the first-level pad layer 3 b are formed by the method similar tothat described with reference to FIG. 8. On the insulating film 2, theinsulating film 4 is formed covering the wiring layer 3 a and pad layer3 b. The upper surface of the insulating film 4 is planarized by CMP.

Similar to the contact holes 7A and 7S described with reference to FIG.10, a small size contact hole 4A and a large size contact hole 4S areformed through the insulating film 4 in the areas corresponding to thewiring layer 3 a and pad layer 3 b. Similar to the contact plug 8 adescribed with reference to FIG. 10, a contact plug 5 a made ofconductive material such as W is formed in the contact hole 4A. Similarto the wiring layer 9 a and pad layer 9 b described with reference toFIG. 10, a second-level wiring layer 6 a and a second-level pad layer 6b are formed on the insulating film 4. The wiring layer 6 a is connectedvia the contact plug 5 a to the wiring layer 3 a, and the pad layer 6 bis directly connected to the pad layer 3 b in the contact hole 4S.

On the insulating film 4, an insulating film 7 is formed covering thewiring layer 6 a and pad layer 6 b. The upper surface of the insulatingfilm 7 is planarized by CMP. A small size contact hole 7A correspondingto the wiring layer 6 a and a large size contact hole 7S correspondingto the pad layer 6 b are formed through the insulating layer 7 byphotolithography and dry etching.

In the semiconductor device shown in FIG. 11, a depth a of the contacthole 7A is smaller than a depth b of the contact hole 7S. During theselective dry etching of forming the contact holes 7A and 7S, it isnecessary to over-etch the contact hole 7A to the depth b after thedepth a of the contact hole 7S is obtained. Therefore, the size of thecontact hole 7A becomes larger than the design value.

In the semiconductor device shown in FIG. 8, the first-level contactholes 4A and 4B have substantially the same depth, and the second-levelcontact holes 7A and 7B also have substantially the same depth. In thesemiconductor device shown in FIG. 9, no contact hole is formed in thebonding pad area. In the semiconductor device shown in FIG. 10, thecontact holes 7A and 7S have substantially the same depth.

In the bonding pad structure shown in FIG. 8, a single bonding pad layer9 b is bonded with a bonding wire. It is therefore not easy to have asufficient bonding pad strength. For example, if an Au wire is bonded tothe pad layer 9 b made of Al alloy, a lowered shearing stress issometimes found by a shear test after the pad layer is exposed to a hightemperature. The reason for this may be ascribed to a thin pad layer 9 band an insufficient supply of Al to the bonded portion (the details ofwhich are to be referred to JP-A-7-335690).

In the bonding pad structures shown in FIGS. 9 and 10, if a laminationfilm including a coated insulating film such as organic or inorganic SOG(spin on glass) is used as the insulating films 4 and 7 or theinsulating film 4 under the pad layer 9 b, peel-off or cracks of thecoated insulating film may occur because of heat and pressure during thebonding, thereby lowering the reliability.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel bonding padstructure of a semiconductor device capable of improving a bonding padstrength by preventing peel-off and cracks of an insulating film,especially of coated insulating film to be caused by heat and pressureduring the bonding and preventing a lowered reliability.

It is another object of the present invention to provide a novel bondingpad structure of a semiconductor device capable of preventing peel-offand cracks of a coated insulating film included in a lamination film tobe used as an interlayer insulating film.

According to one aspect of the present invention, there is provided asemiconductor device comprising: a semiconductor substrate; and abonding pad portion formed on the semiconductor substrate, the bondingpad portion comprising: an insulating film formed on the semiconductorsubstrate and a first-level conductive pad layer of a large island shapeformed on the insulating film; first-level to (n−1)-level (n is aninteger of 3 or larger) interlayer insulating films formed on and overthe insulating film; second-level to n-level conductive pad layersformed on the interlayer insulating films in areas generallycorresponding to an area where the first conductive pad layer wasformed; a plurality of small diameter first through holes from thefirst-level to (n−1) level formed through the first-level to (n−1) levelinterlayer insulating films in areas generally corresponding to an areawhere the first conductive pad layer; a plurality of first contact plugsfilled in the small diameter first through holes from the first-level to(n−1)-level, the first contact plugs at each level being conductive andelectrically connecting two conductive pad layers adjacent along anormal to a surface of the semiconductor substrate, among thefirst-level to n-level conductive pad layers disposed in and on thefirst-level to (n−1)-level interlayer insulating films; an n-levelinterlayer insulating film formed on the (n−1)-level interlayerinsulating film and covering the n-level conductive pad; a largediameter through hole formed through the n-level interlayer insulatingfilm in an area corresponding to an area where the n-level conductivepad was formed, the large diameter through hole having a sizecorresponding to the n-level conductive pad to expose a substantialupper surface of the n-level conductive pad; and a bonding pad formed onthe n-level interlayer insulating film and n-level conductive pad viathe large diameter through hole.

According to another aspect of the present invention, there is provideda method of manufacturing a semiconductor device, comprising the stepsof: (a) forming an insulating film on a semiconductor substrate; (b)forming a first conductive pad layer of a large island shape on theinsulating film; (c) forming a first interlayer insulating film on theinsulating film, the first interlayer insulating film covering the firstconductive pad layer; (d) forming a second conductive pad layer on thefirst interlayer insulating film in an area corresponding to the firstconductive pad layer; (e) forming a small diameter first through holethrough the first interlayer insulating film in an area corresponding toan area where the first conductive pad layer was formed; (f) filling aconductive first contact plug in the small diameter first contact holeto electrically connecting the first and second conductive pad layers;(g) sequentially repeating the steps (c) to (f) to form second-level ton-level (n is an integer of 3 or larger) conductive pad layers andsecond-level to (n−1)-level interlayer insulating films and electricallyconnect two conductive pad layers adjacent along a normal to a surfaceof the semiconductor substrate; (h) forming an n-level interlayerinsulating film on the (n−1)-level interlayer insulating film; (i)forming a large diameter through hole through the n-level interlayerinsulating film, the large diameter through hole having generally a samesize as the n-level conductive pad layer; and (j) forming a bonding padon the n-level interlayer insulating film, the bonding pad beingelectrically connected to the n-level conductive pad layer via the largediameter through hole.

A bonding stress applied to an interlayer insulating film when a wire isbonded to the bonding pad is distributed to a plurality of contactplugs. It is therefore possible to suppress peel-off and cracks of theinterlayer insulating film (coated insulating film) and a highreliability semiconductor device can be realized.

Since the n-level (highest level) pad layer is directly contacted to the(n−1)-level pad layer under the highest level pad layer in the contacthole formed through the (n−1)-level interlayer insulating film under thehighest level interlayer insulating film. It is therefore possible toobtain a bonding pad strength sufficient for bonding a wire to thehighest level (n-level) pad layer.

Furthermore, the upper surface of each interlayer insulating film at thelower-level than the (n−1)-level under the highest level insulating filmis planarized, and the n-level (highest level) pad layer is directlycontacted to the (n−1)-level pad layer under the highest level pad layerin the contact hole formed through the (n−1)-level interlayer insulatingfilm under the highest level interlayer insulating film. Accordingly,the depths of the contact holes in each interlayer insulating film canbe made substantially the same both in the bonding pad area and innerwiring area. It is possible to prevent an undesired increase in the sizeof the contact hole to be caused by an over-etch during the etchingprocess of forming the contact hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a semiconductor device according toan embodiment of the invention.

FIG. 2 is a plan view showing a bonding pad area of the semiconductordevice shown in FIG. 1.

FIG. 3 is a schematic plan view of a semiconductor device, showing aconnection example between bonding pads and internal wiring patterns ofthe semiconductor device shown in FIG. 1.

FIG. 4 is a cross sectional view showing a wiring layer of thesemiconductor device shown in FIG. 1.

FIG. 5 is a cross sectional view showing an interlayer insulating filmof the semiconductor device shown in FIG. 1.

FIG. 6 is a cross sectional view showing an interlayer connectionportion of the semiconductor device shown in FIG. 1.

FIG. 8 is a cross sectional view showing an example of a conventionalsemiconductor device.

FIG. 9 is a cross sectional view showing another example of aconventional semiconductor device.

FIG. 10 is a cross sectional view showing still another example of aconventional semiconductor device.

FIG. 11 is a cross sectional view showing still another example of aconventional semiconductor device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 6 show a semiconductor device according to an embodiment ofthe invention. FIG. 1 is a cross sectional view taken along line X–X′ ofthe plan view shown in FIG. 2. FIG. 3 is a schematic diagram showing theoverall layout of the semiconductor device. The semiconductor deviceshown in FIGS. 1 to 6 will be described by taking as an example afour-layer wiring structure.

On an insulating film 12 made of silicon oxide or the like and coveringthe surface of a semiconductor substrate 10 made of silicon or the like,a first-level (first-layer) wiring layer 14 a and a first-level padlayer 14 b are formed. The first-level wiring layer 14 a is formed in aninner wiring area A including an integrated circuit formed on thesemiconductor substrate 10, and the first-level pad layer 14 b is formedin a bonding pad area B around the area A. A number of bonding pad areasB are disposed surrounding the area A.

The first-level wiring layer 14 a and first-level pad layer 14 b areformed by forming a wiring material layer 14 shown in FIG. 4 on theinsulating film 12 and patterning this wiring material layer 14 byphotolithography and dry etching. For example, the wiring material layer14 is formed by depositing through sputtering a Ti layer 50 having athickness of 15 nm, an Al-0.5 wt % Cu alloy layer 52 having a thicknessof 400 nm, a Ti layer (resistance reducing layer) 54 having a thicknessof 10 nm and a TiN layer (antireflection layer) 56 having a thickness of40 nm in this order from the substrate side. The size of the pad layer14 b is, for example, 70 μm×70 μm.

On the insulating film 12, a first-level interlayer insulating film 16is formed covering the first-level wiring layer 14 a and first-level padlayer 14 b. The first-level insulating film 16 is formed, for example,by the process illustrated in FIG. 5. Namely, on the insulating film 12,a silicon oxide film 60 is formed by plasma CVD, covering thefirst-level wiring layer 14 a and first-level pad layer 14 b. Next,hydrogen silsesquioxane resin is coated on the silicon oxide film 60 byspin coating. This coated film is subjected to heat treatment to form aceramic silicon oxide film 62 having a thickness of about 400 nm in aflat area. In place of hydrogen silsesquioxane, other organic orinorganic SOG may also be used. Thereafter, a silicon oxide film 64having a thickness of 120 nm is formed by plasma CVD, covering thesilicon oxide film 62.

The upper surface of the insulating film 16 is planarized by CMP. Forexample, the silicon oxide film 64 is subjected to CMP to reduce thethickness of the insulating film 16 to a thickness of 800 nm above thefirst-level wiring layer 14 a. A step left in the IC (integratedcircuit) chip area is reduced to about 100 nm. An area of an IC chipobtained by slicing the semiconductor substrate 10 in the unit of eachintegrated circuit is called the IC chip area. In the example shown inFIG. 1, this IC chip area includes the inner wiring area A and a numberof bonding pad areas B disposed around the area A. Etching may beperformed to planarize the first-level interlayer insulating film 16.

Reverting to FIG. 1, a contact hole 16A corresponding to the wiringlayer 14 a and a number of contact holes (e.g., 81 contact holes)corresponding to the pad layer 14 b are formed through the first-levelinsulating film 16 by photolithography and dry etching. For example, ifthe diameter of the smallest contact hole in the area A is 0.35 μm, thediameter of each contact hole 16B is set to 0.35 μm. A number of contactholes 16B are disposed on the pad layer 14 b in a matrix pattern asshown in FIG. 2. A distance between adjacent contact holes 16B is set toa desired value longer than the minimum space determined by the designrule, for example, to 0.65 μm. It is preferable to set the diameter ofeach contact hole 16B to 2D or smaller where D is the diameter of thesmallest contact hole in the internal wiring area A.

Contact plugs 18 a and 18 b made of conductive material such as W areburied in the contact holes 16A and 16B. The contact plug 18 a has thestructure such as shown in FIG. 6. The contact plug 18 b is formed by aprocess similar to that of forming the contact plug 18 a.

In the structure shown in FIG. 6, on the insulating film 16, a Ti layer70 having a thickness of 15 nm and a TiN layer 72 having a thickness of100 nm are sequentially sputtered covering the inner wall of the contacthole 16A. A lamination of the Ti layer 70 and TiN layer 72 functions asa tight contact layer with a W layer 74 to be deposited thereafter. Onthe TiN layer 72, a W layer 74 having a thickness of 500 nm is formed byblanket CVD, burying the contact hole 16A. Thereafter, a lamination ofthe Ti layer 70, TiN layer 72 and W layer 74 is etched back until theupper surface of the insulating film 16 is exposed. In this manner, thecontact plug 18 a made of the Ti layer 70, TiN layer 72 and W layer 74is left in the contact hole 16A. The etch-back may be performed byleaving a lamination of the Ti layer 70 and TiN layer 72 on the uppersurface of the insulating film 16. After the inner wall of the contacthole is covered with the tight contact layer of the Ti and TiNlamination, the W plug is formed. Therefore, an adhesive force betweenthe contact plug and insulating film can be made strong. Since a numberof contact plugs including the tight contact layer are formed, peel-offand cracks of the coated insulating film can be suppressed effectively.

Similar to the wiring layer 14 a and pad layer 14 b, on the insulatingfilm 16, a second-level wiring layer 20 a and a second-level pad layer20 b are formed. The wiring layer 20 a is connected via the contact plug18 a to the wiring layer 14 a, and the pad layer 20 b is connected via anumber of contact plugs 18 b to the pad layer 14 b. The size of the padlayer 20 b may be the same as that of the pad layer 14 b, i.e., 70 μm×70μm.

The wiring layer 20 a is connected to the Ti layer 70, TiN layer 72 andW layer 74 of the contact plug 18 a in the opening of the contact hole16A shown in FIG. 6. This contact state is also applied to a connectionbetween the pad layer 20 b and each contact plug 18 b.

On the insulating film 16, a second-level interlayer insulating film 22is formed covering the wiring layer 20 a and pad layer 20 b. Thesecond-level interlayer insulating film 22 is formed by a processsimilar to that of forming the first-level interlayer insulating film 16described with reference to FIG. 4. The second-level interlayerinsulating film 22 also includes a coated insulating film like thesilicon oxide film 62. The upper surface of the insulating film 22 isplanarized by CMP or the like, similar to the first-level interlayerinsulating film 16.

A small diameter second-level contact hole 22A corresponding to thesecond-level wiring layer 20 a and a number of small diametersecond-level contact holes (e.g., 81 contact holes) corresponding to thesecond-pad layer 20 b are formed through the second-level insulatingfilm 22 by photolithography and dry etching. Second-level contact plugs24 a and 24 b made of conductive material such as W are buried in thesmall diameter second-level contact holes 22A and 22B. The second-levelcontact plugs 24 a and 24 b are formed by a method similar to thatdescribed with FIG. 5 and has the same structure as that of the contactplug 18 a shown in FIG. 5.

Similar to the first-level wiring layer 14 a and first-level pad layer14 b, on the second-level insulating film 22, a third-level wiring layer26 a and a third-level pad layer 26 b are formed. The third-level wiringlayer 26 a is connected via the contact plug 24 a to the second-levelwiring layer 20 a, and the third-level pad layer 26 b is connected via anumber of second level contact plugs 24 b to the second-level pad layer20 b. The size of the third-level (highest level) pad layer 26 b may bethe same as that of the second-level pad layer 20 b, i.e., 70 μm×70 μm.The contact state between the third-level (highest level) wiring layer26 a and second-level contact plug 24 a and the contact state betweenthe third-level (highest level) pad layer 26 b and each second-levelcontact plug 24 b are the same as that between the second-level wiringlayer 20 a and first-level contact plug 18 a shown in FIG. 5.

On the second-level interlayer insulating film 22, a third-level(highest level) interlayer insulating film 28 is formed covering thethird-level wiring layer 26 a and third-level pad layer 26 b. Thethird-level (highest level) insulating film 28 is formed by a processsimilar to that of forming the first-level insulating film 16 describedwith reference to FIG. 5, and includes a coated insulating film like thesilicon oxide film 62. Instead of the coated insulating film like thesilicon oxide film 62, the third-level (highest level) insulating film28 may be made of other films such as a single layer made of a siliconoxide film formed by high density plasma CVD. The upper surface of theinsulating film 28 is planarized by CMP or the like similar to thefirst-level insulating film 16.

A relatively small diameter third-level contact hole 28A correspondingto the third-level wiring layer 26 a and a relatively large diameterthird-level contact hole 28 b corresponding to the third-level pad layer26 b are formed through the third-level insulating film 28 byphotolithography and dry etching. If the diameter of the smallestcontact hole in the inner wiring area A is 0.35 μm, the size of thelarge diameter third-level contact hole 28B may be 65 μm×65 μm.

In the dry etching process of forming the small diameter third-levelcontact hole 28A and large diameter third-level contact hole 28B, theetching conditions such as an etching time are set so that the TiN layerand Ti layer (corresponding to those 56 and 54 in FIG. 4) of thethird-level pad layer 26 b are etched in the third-level contact hole28B and the Al—Cu alloy layer (corresponding to that 52 in FIG. 4) isexposed. With this process, although the Al—Cu alloy layer of thethird-level pad layer 26 b can be exposed in the third-level contacthole 28B, the Al—Cu alloy layer of the third-wiring layer 26 a in thethird-contact hole 28A is also exposed. This exposed Al—Cu alloy layerin the third-contact hole 28A may lower electromigration resistance andform Al hillock.

In order to reliably leave the TiN layer and Ti layer in the smallthird-level contact hole 28A, another etching method may be used.Specifically, the small diameter third-level contact hole 28A and largediameter third-level contact hole 28B are formed by dry etching underthe etching conditions that the TiN and Ti layers of both thethird-level wiring layer 26 a and third-level pad layer 26 b are left.Thereafter, a resist layer is formed by photolithography exposing thebonding pad area B and covering the inner wiring area A. By using thisresist layer and third-level (highest level) insulating film 28 as amask, the TiN and Ti layers of the third-level pad layer 26 b in thelarge diameter third-level contact hole 28B are removed by dry etchingto expose the Al—Cu alloy layer and thereafter remove the resist layer.With this method, lowered electromigration and generation of Al hillockcan be prevented because the Al—Cu alloy layer of the third-level wiringlayer 26 a in the third-level contact hole 28A is not exposed. Referenceis made to JP-A-7-335690 which is incorporated herein by reference.

A small diameter third level contact plug 30 a made of conductivematerial such as W is buried in the small diameter third-level contacthole 28A. This contact plug 30 a is formed by a process similar to thatdescribed with reference to FIG. 5 and has the structure similar to thatof the first-level contact plug 18 a shown in FIG. 5. With the processof etching back the Ti layer, TiN layer and W layer (corresponding tothose 70, 72 and 74 shown in FIG. 5) of the third-level plug 30 a, alamination of the Ti layer, TiN layer and W layer is left on the sidewall of the large diameter third-level contact hole 28B.

A wiring material layer is formed on the insulating film 28, coveringthe lamination 30 b and large diameter third-level contact hole 28B. Forexample, the wiring material layer is formed by depositing throughsputtering a Ti layer having a thickness of 15 nm, an Al-0.5 wt % Cualloy layer having a thickness of 1000 nm and a TiN layer(antireflection layer) having a thickness of 40 nm in this order fromthe substrate side. The deposited wiring material layer is patterned byphotolithography and dry etching to form a fourth-level wiring layer 32a and a fourth-level pad layer 32 b. In this case, the Ti layer having athickness of 15 nm under the Al—Cu alloy layer may be omitted. The sizeof the pad layer 32 b may be 70 μm×70 μm same as that of the pad layer26 b. The wiring layer 32 a is connected via the contact plug 30 a tothe wiring layer 26 a, and the pad layer 32 b is directly connected tothe lamination 30 b and pad layer 26 b in the large diameter third-levelcontact hole 28B. If the Ti layer having a thickness of 15 nm isomitted, Al—Cu alloy layers of the pad layers 26 b and 32 b become indirect contact with each other. Since the lamination 30 b of the Ti, TiNand W layers is left on the side wall of the large diameter third-levelcontact hole 28B while the pad layer 28B is formed, it is possible toprevent the disconnection of the pad layer 32 b at the upper peripheraledge of the large diameter third-level contact hole 28B.

A passivation film 34 is formed on the insulating film 28, covering thewiring layer 32 a and pad layer 32 b. For example, the passivation film34 is formed by depositing a silicon oxide film having a thickness of150 nm and a silicon nitride film having a thickness of 1000 nm byplasma CVD in this order from the substrate side.

A contact hole 34B corresponding to the pad layer 32 b is formed throughthe passivation film 34 by photolithography and dry etching. The contacthole 34B allows a wire to be bonded to the pad layer 32 b, and has asize of, for example, 60 μm×60 μm.

FIG. 7 shows another bonding pad area of a semiconductor device. In FIG.7, like elements to those shown in FIG. 1 are represented by identicalreference symbols, and the detailed description thereof is omitted. Inthis example shown in FIG. 7, the processes up to the process ofplanarizing the upper surface of the interlayer insulating film 22 aresimilar to those described with reference to FIG. 1.

A plurality of relatively small diameter second-level contact holes 22Band a relatively large size contact hole 22C are formed through theinsulating film 22 by photolithography and dry etching. Each relativelysmall diameter second-level contact hole 22B has a diameter of 2D orsmaller where D is the diameter of the smallest contact hole in theinner wiring area A described earlier. The contact hole 22C has adiameter larger than 2D.

By a process similar to the process described with reference to FIG. 6,a plurality of contact plugs are formed in the contact holes 28B. Inthis case, a lamination 24 c similar to the lamination 30 b is left onthe side wall of the contact hole 22C. Generally, in the process ofdepositing and etching back a wiring material layer such as W, thedeposition thickness and etch-back amount of W are determined so that Wis sufficiently filled in the contact hole having the diameter D. Underthese conditions, if the diameter of the contact hole 22C is larger than2D, it is difficult to sufficiently bury W in the contact hole 22C.During the etch-back process, the lamination 24 c is left on the sidewall of the contact hole 22 c and the upper surface of the pad layer 26b in the contact hole 22C is exposed.

A third-level pad layer 26 b is formed by depositing a wiring materiallayer such as the layer 14 shown in FIG. 4 on the insulating film 22 soas to cover the contact plug 24 b, lamination 24 c and contact hole 22 cand by pattering the wiring material layer. The pad layer 26 b directlycontacts the lamination 24 and pad layer 20 b in the contact hole 22C,and is connected to the pad layer 20 b via the contact plug 24 b in thearea other than the contact hole 22C.

By a process similar to that described with FIG. 1, an interlayerinsulating film 28 is formed on the insulating film 22, covering the padlayer 26 b. By a process similar to that described with FIG. 1, acontact hole 28B corresponding to the pad layer 26 b is formed throughthe insulating film 28. By a process similar to that described with FIG.1, a contact plug (corresponding to that 30 a in FIG. 1) is buried inthe contact hole (corresponding to that 28A in FIG. 1), and a lamination30 b is left on the side wall of the contact hole 28B. Thereafter, by aprocess similar to that described with FIG. 1, a wiring material layeris deposited on the insulating film 28 and patterned to form a pad layer32 b. The pad layer 32 b is directly connected to the lamination 30 band pad layer 26 b in the contact hole 28B.

In the bonding pad structure shown in FIG. 7, the pad layer 32 b has arecess 32 c corresponding to the contact hole 22C.

In the bonding pad area B shown in FIG. 1, the small diameter first- andsecond-level contact holes 16B and 22B in the first- and second-levelinterlayer insulating films 16 and 22 are set to have a diameter of 2Dor smaller in order that the contact holes 16B and 22B can be buriedsufficiently with W or the like when a contact hole having a diameter Dis buried with W. Therefore, as shown in FIG. 1, a flat pad layer 32 bwithout a recess such as the recess 32 c can be formed in the contacthole 28B. That a contact hole having a diameter of 2D or smaller can beburied sufficiently with W or the like when a contact hole having adiameter of D is buried with W, is already known (for example, refer toJP-A-9-219451).

FIG. 3 shows an example of a connection between wiring layers 14 a, 20a, 26 a and pad layers 14 b, 20 b, 26 b of the semiconductor deviceshown in FIG. 1.

The wiring layers 14 a, 20 a, 26 a and pad layers 14 b, 20 b, 26 b areconnected together at predetermined levels, e.g., on an insulation film12, on a first-level interlayer insulating film 76, and on asecond-level interlayer insulating film 22, respectively.

On the insulating film 12, the wiring layer 14 a is connected to the padlayer 14 b via a wiring pattern 14 c.

On the first-level interlayer insulating film 16, the wiring layer 20 ais connected to the pad layer 20 b via a wiring pattern 20 c.

On the second-level interlayer insulating film 22, the wiring layer 26 ais connected to the pad layer 26 b via a wiring pattern 26 c.

One wiring layer may be connected to one bonding pad 32 b or two or morewiring layers may be connected if necessary to one bonding pad 32 b.

In the embodiment shown in FIG. 1, when a wire is bonded to the padlayer 32 b, a bonding stress applied to the second-level interlayerinsulating film 22 is distributed to a number of second-level contactplugs 24 b and a bonding stress applied to the first-level interlayerinsulating film 16 is distributed to a number of first-level contactplugs 18 b. It is therefore possible to suppress peel-off and cracks ofthe coated insulating film including both the first- and second-levelinterlayer insulating films 16 and 22.

Since a wire is bonded to the bonding pad layer 32 b in direct contactwith the third-level pad layer 26 b, a sufficient bonding pad strengthcan be realized easily. For example, as described earlier, even if an Auwire is bonded to the bonding pad layer 32 b having the bonding padstructure that the third-level pad layer 26 b and bonding pad layer 32 bboth are made of Al alloy and in direct contact with each other, alowered shearing stress was not found by a shear test after the bondingpad layer was exposed to a high temperature. The reason for this may beascribed to a sufficient supply of Al from the third-level pad layer 26b and bonding pad layer 32 b to the bonding portion.

Furthermore, the depths of the contact holes including the smalldiameter first-, second- and third-level contact holes 16A and 16B, 22 aand 22 b, and 28A and 28B are substantially the same. It is thereforepossible to prevent the size of a contact hole in the inner wiring areaA from being increased by an over-etch during the contact hole etching.

The present invention has been described in connection with thepreferred embodiments. The invention is not limited only to the aboveembodiments. For example, the invention is applicable not only to thefour-layer wiring structure but also to a three-layer wiring structure,a five-layer wiring structure and the like. Wiring material may be Al inplace of Al alloy. It is not necessary that all the pad layers from thelowest to highest levels have a lamination structure of a pad layer anda contact plug. For example, it is obvious that the lamination structuremay be applied to the pad layers from the second-level to the highestlevel. It is apparent that various modifications, improvements,combinations, and the like can be made by those skilled in the art.

1. A semiconductor device comprising: a semiconductor substrate; and abonding pad portion formed on said semiconductor substrate; said bondingpad portion comprising: an insulating film formed on said semiconductorsubstrate; a first-level conductive pad layer of a large island shapeformed on said insulating film; first-level to (n−1)-level (n is aninteger of 3 or larger) interlayer insulating films formed on and oversaid insulating film; second-level to n-level conductive pad layersformed on said interlayer insulating films in areas generallycorresponding to an area where said first conductive pad layer wasformed; a plurality of small diameter first through holes from thefirst-level to (n−1) level formed through said first-level to (n−1)level interlayer insulating films; a plurality of first conductive plugsfilled in said small diameter first through holes from the first-levelto (n−1)-level, said first conductive plugs at each level beingconductive and electrically connecting two conductive pad layersadjacent along a normal to a surface of said semiconductor substrate,among said first-level to n-level conductive pad layers disposed on saidinsulating film, and first-level to (n−1)-level interlayer insulatingfilms; an n-level interlayer insulating film formed on said (n−1)-levelinterlayer insulating film and covering said n-level conductive padlayer; a large diameter through hole formed through said n-levelinterlayer insulating film to expose an area of said n-level conductivepad layer; and a bonding pad formed on said n-level interlayerinsulating film and n-level conductive pad layer via said large diameterthrough hole, wherein said small diameter first through holes includeones located in a peripheral area outside of said large diameter throughhole.
 2. The semiconductor device according to claim 1, wherein saidsmall diameter first through holes are substantially uniformlydistributed in an area defined by said large diameter through hole andsaid peripheral area.
 3. The semiconductor device according to claim 1,wherein said small diameter first through holes are substantiallyuniformly distributed in a direction normal to a surface of saidsemiconductor substrate.
 4. The semiconductor device according to claim1, further comprising a wiring portion comprising: the insulating filmformed on the semiconductor substrate; the first-level to (n−1)-levelinterlayer insulating films formed on the insulating film; first-levelto n-level wiring layers formed on and over said semiconductor substrateat same levels as said first-level to n-level conductive pad layers;small diameter second through holes from the first-level to (n−1)-level,formed through said first-level to (n−1)-level interlayer insulatingfilms; and a plurality of second conductive plugs filled in said smalldiameter second through holes from the first-level to (n−1)-level, saidsecond conductive plug at each level being conductive and electricallyconnecting two wiring layers adjacent along a normal to the surface ofsaid semiconductor substrate, among said first-level to n-level wiringlayers disposed on said insulating film, and first-level to (n−1)-levelinterlayer insulating films.
 5. The semiconductor device according toclaim 4, further comprising wiring patterns for connecting said bondingpad layer and said wiring layer at a same-level.
 6. The semiconductordevice according to claim 5, wherein said interlayer insulating filmincludes a coated insulating film.
 7. The semiconductor device accordingto claim 6, wherein said bonding pad portion is formed around saidwiring portion.
 8. The semiconductor device according to claim 6,wherein said conductive pad layer includes a Ti layer, an Al—Cu alloylayer and a TiN layer.
 9. The semiconductor device according to claim 6,wherein said conductive pad layer includes an Al—Cu alloy layer and aTiN layer.
 10. The semiconductor device according to claim 6, wherein adiameter of said small diameter first through hole is two times orsmaller than a diameter of said small diameter second through hole. 11.The semiconductor device according to claim 6, wherein said first andsecond conductive plugs are made of W.
 12. The semiconductor deviceaccording to claim 6, wherein said first and second conductive plugseach comprise: a first layer of Ti, Ti/TiN or TiN covering an innersurface of each of said small diameter first and second through holes;and W layer formed thereon.
 13. The semiconductor device according toclaim 6, wherein said interlayer insulating film contains silicon oxide.14. The semiconductor device according to claim 6, wherein a siliconoxide film and a silicon nitride film are formed on said n-levelinterlayer insulating film.